U.S. Patent Application US 2004/0263960 discloses a stereomicroscope that has multiple light-emitting diodes provided on a planar carrier for illumination. A further illumination device made up of light-emitting diodes is additionally provided, for oblique illumination, in the focusing arm in the vicinity of the objective opening. A third illumination device having light-emitting diodes is embodied in annular fashion and is mountable around the objective opening of the stereomicroscope. A substantial disadvantage of the illumination device that is arranged around the objective opening of the stereomicroscope is that it represents a separate element and thus can easily be lost or stolen.
German Unexamined Application DE 39 06 555 A1 discloses an incident-light specimen illumination device. The incident-light specimen illumination device encompasses multiple individual switchable light sources (self-luminous elements, glass fibers, or apertures illuminated from behind). The light sources are advantageously arranged in multiple concentric circles in different planes, from which light is emitted with different radiation axes. Illumination is thus possible at different selectable illumination angles with no mechanical displacement of light sources or imaging elements. The individual light sources are secured in a semi-spherical carrier. The carrier is arranged around the objective of the microscope or of the observation device.
German Utility Model DE 298 09 759 U1 discloses an apparatus for medical treatment using a light source. The light sources for illumination of a surgical field are embodied as light-emitting diodes, and are arranged so that the radiation emitted by them strikes the surgical field at an angle of between 5° and 80° with respect to an optical axis. This apparatus says nothing, however, about the setting of different illumination conditions, and does not mention that the light-emitting diodes can be used in the illumination system for a microscope or a stereomicroscope.
German Unexamined Application DE 100 30 772 A1 discloses an arrangement and a method for illumination, in particular for incident illumination, in microscopes having an annular carrier, oriented around the optical axis, for the reception of illuminating means. The light-emitting diodes are mounted on the annular carrier in at least two concentric circles. The annular carrier is arranged symmetrically about the optical axis of a microscope objective. The light-emitting diodes possess a relatively small emission angle, and are directed or tilted toward the optical axis of the microscope. White-light LEDs are used as diodes. The LEDs can likewise be connected together in groups, and are operated via a controllable constant-current source. A disadvantage here as well is that the light-emitting diodes are mounted on a separate carrier that once again is easy to misappropriate or easy to lose.